For many years there has been a desire by the Defense Department to have a non-nuclear means of attacking underground facilities. Present technology is inadequate to this task because of the inability to penetrate deep enough in to the earth to reach the facility or to get deep enough to deliver a sufficiently large explosive quantity to generate sufficient shock in the overburden to collapse underground caverns.
Previous methods used for deep penetration explosive include a “hard-nosed” kinetic energy penetrator with explosive inside, essentially a penetrator bomb. The latest version of this device weighs 30,000 lbs. Two-thirds or more of the weight of this penetrator is parasitic, but this additional weight is required to make this device robust enough to survive its impact with and penetration of hard surfaces, such as reinforced concrete or solid rock.
Known penetrator weapons are dropped from high altitude and perhaps rocket-boosted to high velocity and slammed into the earth. The outer casing, the high explosive charge, and delicate fusing in this warhead must survive this impact and operate as designed upon reaching its maximum depth. This sledgehammer approach to penetrating deep into hard rock or multiple layers of concrete is ineffective against targets that are protected by more than 100 feet of hard rock or solid concrete.
Some effort has been made with placing a conventional shaped charge ahead of the projectile in order to create a pilot hole in the rock; however, only a small gain in depth of penetration is achievable with this method because of the very small hole diameter produced by a conventional shaped charge. The hole diameter made by a conventional shaped charge jet is small, on the order of one-tenth the diameter of the explosive charge forming the jet, and it penetrates approximately 6-8 times the diameter of the charge in steel (more in rock or masonry). A kinetic penetrator weapon could see some small advantage from this shaped charge pilot hole but will still experience tremendous ballistic shock and deceleration and will have a difficult time penetrating more than 100 feet in solid material.
This requires the projectile penetrator to have a massive outer case, which accounts for ⅔ of the weapon's weight. This earlier projectile weapon is slender; it has approximately a 10-to-1 length-to-diameter ratio, limiting the amount of high explosive onboard, as well as its orientation and coupling to the overburden. When prior art warheads are detonated, its cross-sectional “footprint” is only the diameter of the weapon, and the length of the explosive load is perpendicular to the desired shock direction.
Another type of deep penetration weapon is mostly effective against layered concrete facilities like underground basements or buildings such as Saddam Hussein's hiding place in Baghdad, which the U.S. military attacked with a smaller weapon of this kind. A BLU-57 penetrator weapon is very heavy because of the requirements of the task and requires a special aircraft to deliver it. Penetrating 80 to 100 feet is possible with a kinetic energy projectile if it has sufficient velocity, durability and mass to remain intact in its abrasive travel through the target material.
As this penetrator weapon pushes its way through the rock or concrete, the forces created radially put the target material in compression, as it has to move the material perpendicular to its direction of travel to make the hole it needs. In layered structures, the material in front of the weapon is pushed into the empty space ahead so that there is not as much resistance. In the penetration of solid materials, the material restricting the travel of the penetrator can only go lateral or aft, creating a much more difficult task than layered material. If a facility is buried in a mountain with hundreds of feet of hard rock above it, then clearly one needs a different approach.